1. Field of the Invention
The present invention relates to the oxidation of substituted phenols to form quinones, and more particularly to the oxidation of such compounds by means of an oxygen-containing gas in the presence of a salcomine catalyst.
2. Description of the Prior Art
The synthesis of quinone, e.g., benzo- and diphenoquinones, by the catalytic oxidation of phenols in the liquid phase has been widely reported. Catalysts which have been found useful in this synthesis include soluble copper-nitrile complexes (U.S. Pat. No. 3,987,068) and salcomines (Van Dort, H. M., et al., Rec. trav. chim. 86, 520-526 (1967); Vogt, L. H., Jr., et. al., J. Org. Chem. 34, 273-277 (1969); Kothari, V. M., et al., J. Catalysis 41, 180-189 (1976); U.S. Pat. Nos. 3,859,317 and 3,966,776).
While the salcomine-catalyzed oxidation is attractive for the synthesis of certain 1,4-quinones because it affords high selectivity for the desired product and presents fewer corrosion problems than are encountered in other catalyst systems, the process as heretofore practiced has attracted little commercial interest because of the relatively small amount of quinone produced per mole of catalyst. In the past, the salcomine catalyst became totally, and apparently irreversibly, inactive after a number of oxidation cycles which was too small to overcome its relatively high price.